Bernie Sanders names the one thing Democrats should not do if they want to defeat Trump in 2020

Sen. Bernie Sanders said if 2020 Democrats spend all of their time attacking President Donald Trump along the campaign trial, it will ultimately hurt them at the ballot box.

"If we spend all our time attacking Trump, you know what, Democrats are going to lose," Sanders said. "Our job is to lay out a vision that makes sense to the working families of this country."

Sanders was asked questions on a variety of issues, but he went into particular detail on his healthcare plan.

At one point, a Fox News moderator asked the audience to raise a hand if they would be "willing to transition" from their private healthcare plans to what Sanders is proposing with "Medicare for All." Many across the room cheered and raised their hands.

Sen. Bernie Sanders on Monday said if he and other 2020 Democrats spend all of their time attacking President Donald Trump, then they will lose the election.

"Whether you're conservative or moderate or progressive, I don't think the American people are proud that we have a president who is a pathological liar. It does not give me pleasure to say that ... Trump cannot even tell the truth as to where his father was born," Sanders said during a Fox News town hall.

But then he issued a warning to his fellow 2020 Democrats.

"If we spend all our time attacking Trump, you know what, Democrats are going to lose," Sanders said. "Our job is to lay out a vision that makes sense to the working families of this country."

Sanders went after Trump several times over the course of the evening — including on the issue of releasing tax returns, a matter that the president has received criticism for before and after his election.

But much of the town hall was focused on Sanders' platform and what it would mean for the country as the senator has emerged as the early front-runner in a crowded, diverse field of Democratic candidates.

The Vermont senator was asked questions on a variety of issues over the course of the evening from the Fox News moderators Bret Baier and Martha MacCallum, as well as audience members. Baier said the audience was mixed with Democrats, Republicans, independents, and democratic socialists.

Over the course of the town hall, Sanders made the case for why voters should not fear tax hikes from "Medicare for All," outlined his foreign-policy vision, explained why he's so concerned about climate change, and championed comprehensive immigration reform.

At one point, Baier asked the audience to raise a hand if they would be "willing to transition" from their private healthcare plans to what Sanders is proposing with Medicare for All.

Many across the room cheered and raised their hands.

Sanders conceded to the moderators his healthcare plan would involve hiking taxes but said healthcare costs would be lower overall because "they're not paying premiums, copayments, and deductibles."

The senator is calling for universal healthcare under his Medicare for All plan, which would provide every American with health insurance via Medicare and eliminate private insurers. A recent INSIDER poll found voters are fairly split on Sanders' healthcare plan, with 43% in favor of it and 45% opposing Medicare for All.

At the end of the town hall, Sanders told the moderators he hoped he wasn't too hard on them and offered his final thoughts to audience members.